The hydroxylase component (MMOH) of methane monooxygenase, which is found in methanotropic bacteria, catalyzes the remarkable conversion of methane to methanol utilizing dioxygen and reducing equivalents of NAD(P)H. The R2 subunit of ribonucleotide reductase triggers the conversion of ribonucleotides to deoxyribonucleotides, which is an essential step in DNA biosynthesis. Despite their different functions in Nature, the two metalloenzyme both utilize a diiron core, and their catalytic cycles are though to proceed via similar reaction pathways. Our long-term goal is to achieve an understanding of the mechanisms employed by these two important metalloenzyme for performing O-O and C-H bond activations. The propose work starts with the syntheses of complexes which model proposed intermediates in the catalytic cycles of MMOH and R2. Full characterization of these models will give data for the evaluation of the proposed intermediates, for which there is little or no small-molecule precedence. In addition to synthesis and characterization, we intend to use the reactive model complexes to carry out mechanistic studies of processes which mimic important steps in the catalytic cycles of the metalloenzyme. From these studies we hope to gain insight into the mechanisms employed during O-O and C-H bond activations.